To determine the database consistency in a hierarchical database, it is typically necessary to calculate a sum value of retention addresses of respective segment data included in the database and a sum value of pointers included in the database and to determine whether there is a match between the sum values. If a database is updated during the time from starting the readout of one pointer until completing (or prior to completing) the readout of all the pointers, the sum value would be calculated with the pointer values used before and after the update mixed with each other, thereby sometimes causing an error in determining the consistency.
Therefore, it has been a common practice to stop updating a database or to exclusively control access to at least a part of the database during the process of determining the consistency (see, for example, Japanese Published Patent Application H8-249222). If the data size of the database is large, however, the update processing is generally halted for a large amount of time or the update processing is significantly delayed, which sometimes leads to a reduction in user-friendliness. Accordingly, there has been suggested a technique for determining the consistency without halting the update processing (see Japanese Published Patent Application 2001-142765).
In the technique of Japanese Published Patent Application 2001-142765, the determination process is performed several times without performing exclusive control with respect to other processes. Then, it is determined, based on the result of the determination performed several times, whether it is highly probable that there is consistency. Therefore, this technique cannot determine the consistency reliably and the result of determination of the consistency varies depending on other processes being performed during the process of consistency determination.